One of the major deficiencies of currently available composite restoratives is the lack of marginal integrity caused by polymerization shrinkage. The investigations described in this proposal are designed to evaluate the potential of modifying a commercially available light cured cycloaliphatic epoxy for use as a resin matrix for dental composites. The unfilled cycloaliphatic epoxies exhibit volumetric curing shrinkages of 1-2 percent compared to the 2-6 percent reported for current dental composite formulations. The major thrust of the work will modify the available catalyst system to be compatible with conventional dental light sources and evaluate the biocompatibility of these materials. Basic mechanical and physical properties of cured samples will be used to optimize the curing chemistry and evaluate heir potential as dental restoratives. Fibroblast cytotoxicity of the resin/catalyst system will be determined and used to assess the biocompatibility of experimental systems.